This invention relates to polymer processing systems. In particular, the invention is concerned with those systems which treat amorphous polyester to achieve crystallization followed by solid phase polymerization, followed by cooling. An example of such a system is found in Herron U.S. Pat. No. 4,161,578.
In systems of the type contemplated by this invention, cold amorphous polymer material is fed to a crystallizer and, after substantial heat input, hot product is discharged. The particular apparatus for achieving the crystallization may comprise an indirect heat supply unit or a fluid bed. The SOLIDAIRE.RTM. or TORUSDISC.RTM. equipment manufactured by Hosokawa Bepex Corporation of Minneapolis, Minn. is an example of an indirect heat supply unit which may be utilized for achieving the crystallization. In such a system, steam or other heated fluid is passed through rotors and/or jackets being in contact with the agitated polymer material. The polymer is thereby brought into contact with these hot surfaces and heated to the necessary temperature for achieving the crystallization reaction.
In a fluid bed system, for example units manufactured by Hosokawa Bepex, heated air is brought into contact with the polymer material. In order to improve heat transfer and to achieve the temperatures required for the crystallization reaction, it is preferred that indirect heating elements in the form of tube bundles or plate coils be immersed in the fluidized material.
In systems of the type described, the crystallized material is transferred to a reactor for achieving polymerization. Subsequent to the polymerization, the material is transferred to a cooler which may also comprise, for example, a TORUSDISC.RTM. or fluid bed system. In this stage of the operation, the rotors, jackets or coils are supplied with cold heat transfer liquid to achieve the heat exchange necessary for cooling the product prior to discharge from the cooler.
In a typical operation of the type described, the steam or other heat transfer media employed for the crystallization stage is condensed and directed out of the system, for example, for use in a steam generator. Similarly, any heat values picked up by the liquids used during the cooling operation may be lost, or at least recovered only outside of the polymer processing system.